This invention relates to fuel flow in a carburetor for an internal combustion engine and more particularly to controlling the flow of fuel throughout a wide range of engine load conditions.
Fuel flow in a carburetor is usually controlled by positioning a fuel metering rod in an orifice between the carburetor's fuel bowl and a fuel passage through which fuel is drawn from the bowl to an air passage where it mixes with air to produce a mixture combusted in the engine on which the carburetor is installed. The position of the rod in the orifice is determined by a number of factors, among these being throttle valve position, engine load as evidenced by the engine vacuum level and atmospheric pressure (altitude). Thus, as the throttle valve opens or closes, more or less fuel, respectively must be supplied through the fuel passage; while if the throttle position is constant and the engine load changes, as when a vehicle starts up a hill, the position of the metering rod is varied to adjust or modulate the quantity of fuel supplied through the fuel passage for that throttle valve position. Because of the wide range in engine vacuum which occurs between engine starting, curb idle, normal cruise and wide-open throttle conditions; it has not been possible in the past to provide the range of metering rod movement necessary to obtain satisfactory fuel flow control for all conditions. The ability to modulate fuel flow during cruise conditions, for example, may prevent adequate control during starting so that less fuel is available for mixing with air and an insufficiently rich air-fuel mixture is supplied to the engine, making it difficult to start the engine.